Teamlets?dyadsconsistingofaphysicianandstaffmemberwhoconsistentlyworktogether?maypro- videasimple,efficientwaytoreorganizeprimarycaretocreatehigherqualityandimprovepatient,phy- sician, and staff experience. But little funding or policy attention has been given to teamlets;? there is no quantitative evidence on their prevalence and characteristics and no large scale study of their relation- shiptothequalityandcostofcare.Thelong-termgoalofthisprojectistohelpimproveprimarycareby discovering,evaluating,anddisseminatinginformationonhigh-performingprimarycaremodels.Thekey objectivesofthismixedmethodsprojectaretoassesstheprevalenceandcharacteristicsofprimarycare teamletsintheU.S.,todeterminetherelationshipbetweencaredeliverybyateamletandthequalityand cost of care and physician burnout, and to identify the configurations? the cluster or clusters of charac- teristics?typicalofhigh-performingteamlets.Thecentralhypothesesare(1)thequalityofcareishigher andtotalspendingoncareislowerforMedicarebeneficiarieswhoarepatientsofprimarycareteamlets;? (2) burnout is less likely in physicians who work in teamlets;? (3) teamlet performance increases with the numberofyearsthattheteamlethasworkedtogether?atleastuptoacertainnumberofyearsand(4) thatcertainconfigurationsofcharacteristicsdifferentiatehigh-performingteamlets.Thespecificaimsare (1) to determine the prevalence and characteristics of primary care teamlets in the U.S.;? (2) determine therelationshipofprimarycareteamletstothequalityandcostofcareandtophysicianburnout,and(3) identify the configurations of characteristics of high-performing primary care teamlets. Methodologically, the project will (1) survey a large random national sample of primary care physicians to determine the prevalenceofteamlets,theircharacteristics,thepredictorsofphysicianparticipationinateamlet,andthe relationshipofteamletstophysicianburnout;?(2)linkthesurveytoMedicareclaimsdatatocomparethe performance of physicians in teamlets to physicians not in teamlets for important outcomes of care;? (3) interview a stratified random sample of teamlets to provide depth of understanding of teamlets and of barrierstotheircreationandsuccess;?and(4)useaninnovativemethod?QualitativeComparativeAnal- ysis?todeterminetheconfigurationsofcharacteristicsthatappeartobenecessaryand/orsufficientfor ateamlettobehigh-performing.Theprojectwillprovidethefirstlargescale,criticalevidenceonwhether primary care teamlets improve care, on the characteristics of high-performing teamlets, and on barriers toandfacilitatorsofcreatingeffectiveteamlets.Thisevidence?thefirstofitskind?willbeusefultopoli- cymakers, leaders of provider organizations, physicians, and researchers trying to determine effective waystoconfiguretheprimarycareworkprocess.